The moderate size, direct-view CRT display which is in general use is generally considered superior to other display methods. The CRT has wide color range and high purity, thereby providing vivid images. It has gray scale fidelity, a wide viewing angle and provides good display of motion. It can provide high resolution with sharpness of detail and adequate overall efficiency. It has also been substantially the lowest cost display available. Its one substantial negative characteristic is its bulk--especially depth and, consequently, its weight. Exacerbating this negative feature are two trends of major significance to the instant invention.
1--Recent consumer preference has been for larger display size, partially responding to high definition television (HDTV) development, which also calls for higher resolution and a wider aspect ratio.
2--Improvements in IC memory, logic and control chips, which store, process and scan-convert between media standards, as well as improved signal transmission means is rapidly leading to demand for multi-media access via information display. Again the pressure is for higher resolution and increased display size parameters.
The increased size of a conventional CRT adds bulk and further requires higher electron beam performance to maintain brightness and resolution. Illustrative of this is that demand has been met by more complex and expensive CRT projection units. There is even demand for the large and very bulky direct view CRT, and the technology to meet the contemplated size, wide view angle, and resolution of HDTV is still evolving.
The improvements in electronic elements is also illustrated by HDTV, which has developed a very efficient digital signal capable of scan conversion flexibility. Another improvement, sometimes referred to as tiling, allows stacking of a number of standard displays to make a large display. In these display subsections, the framing is made as narrow as possible, but the display appears as if seen through a heavy grid. Scan conversion divides the large picture's information into properly selected segments fed to respective subsections. In one example shown in U.S. Pat. No. 5,635,105, the tiles are partially deleted by combining a row of small sub-elements in one bulb. But these prior art examples do not have the means for precisely matching the subsections to make their borders invisible, or substantially so, even where they are not framed.
Two examples will illustrate the state of the art of displays to which this disclosure may be applied. Transmission standards for high definition television (HDTV) are rapidly being promulgated. Some optimum utilization calls for large size and approximately 1000 line resolution. The ratio is 16/9 (1.8/1) as compared to 4/3 for NTSC. The larger aspect ratio and/or increase in display size leads rapidly to excess depth, bulk and weight for direct view CRT systems and to higher power requirements and to extreme difficulty in achieving high resolution. Thus, the cost becomes excessive.
Current demand for larger size was initially met by color projection sets having three projection tubes. These have not yet achieved the size or resolution expected for HDTV but their size is quite adequate for much typical viewing. However, it is interesting to note that large-size, direct-view sets, e.g., up to about 36" diagonal, have more recently become available. In spite of bulk there is some customer preference for direct view over projection sets of similar or even larger size.
The second example pertains to computer terminals. There is demand for larger, high resolution displays for graphics and for the capability to display two standard 8.5.times.11" full pages. Again, the aspect ratio can be about 1.5/1 (standard 35 mm film). In this case, display depth and bulk is again at a premium, and demand is often met by flat displays at a much higher price. These examples will be used to describe preferred embodiments of this invention.